1. Field of the Invention
The present invention relates to a semiconductor light-emitting element, and particularly to a GaN light emitting diode having a high light-emitting efficiency by doping boron atoms in the window layer.
2. Description of the Prior Art
A light emitting diode (LED) is a photoelectric element made of semiconductor material. This element has two electrode terminals, and a voltage is exerted between the terminals and little current passes through them so as to emit light. In order words, the emitting principle of LED is to exert a voltage on the composition semiconductor made of AlGaAs, AlGaInP, and GaInN, all of which are belonged to III-V group, so that the electron will be combined with the electric hole and the excessive energy will be releases so as to emit light.
In order to achieve a high efficiency, the crystallization is promoted so as to increase the inside quantum efficiency, and in addition, the improvement of the light extraction technology and the light-emitting efficiency can increase the practical usage of the LED. In the prior art light emitting diode, the refraction coefficient of the GaN is 2.3, and the refraction coefficient of the air is 1.0. Therefore, the light emitted from the function layer of the diode is easily refracted and re-absorbed. This will make the light emitting efficiency of the light emitting diode poor. In order to improve the light emitting efficiency, a light emitting diode is developed to have a window layer, made of semiconductor material, for penetrating the light so that the light emitting efficiency can be increased. However, this will make the manufacture cost high and take much time for manufacture so that the price of the diode is very high.
Therefore, the present invention is provided to resolve the mentioned problems. By doping proper amount of borons in the material of the window layer of the GaN-based composition semiconductor light-emitting element, the refraction coefficient of the window layer can be reduced so that that refraction coefficient is more approaching the refraction coefficient of the air. Therefore, the re-absorption efficiency can be reduced so as to promote the light emitting efficiency of the GaN light emitting diode.
The main objective of the present invention is to provide a GaN-based composition semiconductor light-emitting element and its window layer structure. By appropriately doping borons in the window layer of the GaN light-emitting element, the activity rate of the P type doping will be increased so that the refraction coefficient of the window layer can be reduced so as to be more approaching to that of the air. Therefore, the refraction can be reduced and the light emitting efficiency will be promoted so as to overcome the problems of the prior art caused by the poor light emitting efficiency.
Another objective of the present invention is to provide a GaN-based composition semiconductor light-emitting element and its window layer structure. By increasing the thickness of the window layer, the light emitting efficiency of the light-emitting element will be increased and the generation probability of the defect will also be reduced.
In order to achieve the above objectives, the GaN-based composition semiconductor light-emitting element according to the present invention comprises a light-emitting epitaxy layer made of GaN-based composition, and a window layer formed on the light-emitting epitaxy layer. This window layer is made of GaN-based composition and is doped with boron atoms. The composition ratio of the boron atoms is lower than three-tenths in the GaN-based composition. Therefore, the refractive index of the window layer is lower than the refractive index of the light-emitting epitaxy layer.
According to the present invention, the window layer comprises a first window layer and a second window layer below the first window layer. The two window layers are made of BxAlyGazN, wherein 0xe2x89xa6xxe2x89xa61, 0xe2x89xa6Yxe2x89xa61, 0xe2x89xa6zxe2x89xa61, and x+y+z=1, where x is the composition ratio of boron. The first window layer is formed under a low temperature while the second window layer is formed under a high temperature. In addition, the first and second window layers also can be separately formed under high temperatures.
In order to achieve the mentioned objectives, the present invention provides a window layer structure for a GaN-based composition semiconductor light-emitting element. This window layer structure is formed on several epitaxy layers, and the window layer is made of GaN-based composition. Boron atoms are doped in the window layer and the composition ratio of the borons is lower than three-tenths in the GaN-based composition so that the refractive index of the window layer is lower than the refractive indexes of the epitaxy layers.